Ethanol manufactured from biomass is lower alcohol fuel that plays important role in reduction of CO2 emission. Examples of biomass ethanol that has been commercially practical includes the ones obtained by ethanol fermentation of starch sugar from sugarcane, corn, or the like.
Cellulose, which is biomass resource, mainly constitutes lignocellulose (ligneous resource). As with cellulose, lignin is a major component in the support structure of a woody plant. In recent years, attention has been focused on woody biomass such as a woody plant, and research has been made on the technique of efficiently generating glucose from a woody plant and manufacturing ethanol from glucose derived from a woody plant. Especially, the technique of manufacturing monosaccharide or oligosaccharide from lignocellulose composed of cellulose and lignin has been developed.
For the manufacture of paper and/or pulp and the use of lignocellulose as a material for sugars, it is necessary to obtain cellulose by disaggregating or disassembling lignin that firmly bonds to cellulose from lignocellulose. However, enormous amounts of time and cost are required for the disaggregation/disassembly of lignin. As such, there has been demand for the production of trees containing low lignin content.
A technique of modifying lignin content and/or cellulose content in a plant is known. Especially, phenylpropanoid biosynthesis pathway that is lignin biosynthesis pathway has received attention (see Patent Documents 1 and 2, for example). Patent Document 1 discloses that lignin content in a plant is reduced by suppressing the function of a transcription factor promoting the expression of an enzyme that functions in phenylpropanoid biosynthesis pathway. Patent Document 2 discloses a technique of transforming a plant with a plurality of genes derived from phenylpropanoid biosynthesis pathway.
Further, a technique of reducing lignin biosynthesis while increasing cellulose biosynthesis by causing a plant to express an enzyme related to cellulose synthesis pathway is also known (see Patent Document 3).
[Patent Document 1]
    Japanese Unexamined Patent Publication No. 276181/1999 (Tokukaihei 11-276181, published on Oct. 12, 1999)[Patent Document 2]    Japanese PCT National Phase Unexamined Patent Publication No. 515224/2004 (Tokuhyo 2004-515224, published on May 27, 2004)[Patent Document 3]    Japanese PCT National Phase Unexamined Patent Publication No. 509009/2003 (Tokuhyo 2003-509009, published on Mar. 11, 2003)[Patent Document 4]    Japanese Unexamined Patent Publication No. 269177/2001 (Tokukai 2001-269177, published on Oct. 2, 2001)[Patent Document 5]    Japanese Unexamined Patent Publication No. 269178/2001 (Tokukai 2001-269178, published on Oct. 2, 2001)[Patent Document 6]    Japanese Unexamined Patent Publication No. 292776/2001 (Tokukai 2001-292776, published on Oct. 2, 2001)[Patent Document 7]    Japanese Unexamined Patent Publication No. 292777/2001 (Tokukai 2001-292777, published on Oct. 23, 2001)[Patent Document 8]    Japanese Unexamined Patent Publication No. 269176/2001 (Tokukai 2001-269176, published on Oct. 2, 2001)[Patent Document 9]    Japanese Unexamined Patent Publication No. 269179/2001 (Tokukai 2001-269179, published on Oct. 2, 2001)[Patent Document 10]    International Publication No. WO03/055903, pamphlet (published on Jul. 10, 2003)[Patent Document 11]    Japanese Unexamined Patent Publication No. 278422/2005 (Tokukai 2005-278422, published on Oct. 13, 2005)[Non-Patent Document 1]    Mitsuda, N., Seki, M., Shinozuka, K. and Ohme-Takagi, M., The Plant Cell, Vol. 17, 2993-3006, November, 2005[Non-Patent Document 2]    Ohta, M., Matsui, K., Hiratsu, K., Shinshi, H. and Ohme-Takagi, M., The Plant Cell, Vol. 13, 1959-1968, August, 2001[Non-Patent Document 3]    Hiratsu, K., Ohta, M., Matsui, K., Ohme-Takagi, M., FEBS Letters 514 (2002) 351-354